Millions of bacteria live in your stomach. The bacteria benefit by being able to eat what you eat! You benefit because the bacteria help break down food you otherwise could not have broken down. This is an example of what kind of symbiotic relationship?

the index of refraction of the second medium is higher. i just took the test trust me !

the second type of galaxy is called a barred spiral, which has a thing called a bar straddling the nucleus

the menstrual cycle – higher tier. negative feedback mechanisms affect the production of hormones in the menstrual cycle. oestrogen also stimulates the release of lh (luteinising hormone) from the pituitary gland, which in turn controls the production of progesterone.